The present invention relates to a recording and a reproduction apparatus, a recording and a reproduction method, and a recording and a reproduction program for information to be embedded in digital image data. Particularly, this invention relates to a recording and a reproduction apparatus, a recording and a reproduction method, and a recording and a reproduction program for imperceptible information to be embedded into digital image data by, for example, electronic watermarking, the embedded information being used for determining whether digital image data has been tampered with, especially, in determination of copyright violation when the embedded information is used as copyright information.
With distribution of digital content, images, music, etc., over a communication network, such as, the Internet, becoming popular, several types of technique of embedding an encoded electronic watermarking signal in a digital signal of the content have been proposed for protection of the content against illegal duplication or tampering.
For example, the following three literatures disclose electronic watermarking.
(1) Japanese Unexamined Patent Publication No. 2000-287065
(2) Non-patent literature “A Copyright Information Embedding Method using DCT (Discrete Cosine Transform) for Digital Movies”, SCIS' 97-31G, The 1997 Symposium on Cryptography and Information Security, Fukuoka, Japan, Jan. 29-Feb. 1, 1997, The Institute of Electronics, Information and Communication Engineers
(3) Non-patent literature “A Watermarking Scheme to Image Data by PN Sequence”, SCIS' 97-26B, The 1997 Symposium on Cryptography and Information Security, Fukuoka, Japan, Jan. 29-Feb. 1, 1997, The Institute of Electronics, Information and Communication Engineers
In detail, the Japanese Unexamined Patent Publication (1) discloses an image processing system equipped with an image processing unit and an image display device.
The image processing unit provides an original picture resulting from embedding electronic watermark information that can be extracted by using a watermark key, including authentication information which authenticates an image file from a legal server into an original image and provides the watermark key.
The image display device uses the watermark key served by the image processing unit, extracts the electronic watermark information from the original image, stores the original image whose falsification is discriminated by using the watermark key and the watermark key itself, extracts the electronic watermark information from the served original image by using the watermark key served the by an image management server properly serving the original image and the watermark key to a utility destination, and displays the original image whose falsification is discriminated by using the authentication information of the watermark key for a purpose of browsing.
The non-patent literature (2) discloses a new watermarking method which is suitable for MPEG bit stream. The method based on modifying DCT coefficients are better than the method based on modifying the other domain such as motion vectors or quantizer matrices against erasing copyright information attack using editing or compression.
The non-patent literature (3) discloses a data hiding method which uses a PN sequence in the spread spectrum technique. An arrow band signal to stand for a signature is set to a wideband channel of which an image is spread. When converting the spread spectrum to the normal image by PN sequence, inversely, the signature is embedded in wideband channel, which is low in power. Thus, the signature does not give serious damage to the image.
According to the electronic watermarking information embedding techniques described above, electronic watermarking information is recorded through a specific recording or encoding processing so that visual inspection of conversion of image data is almost impossible. The recorded electronic watermarking information is extracted through processing which is the inverse of the recording or encoding processing. It is thus determined whether the image data has been tampered with by checking the extracted electronic watermarking information, irrespective of the type of image-data delivery mechanism (via computers network or storage medium).
Nevertheless in these electronic watermarking information embedding techniques, electronic watermarking information is usually selectively embedded into some local areas of one frame image not in the entire frame image.
This leads to a trouble in that the electronic watermarking information remains unchanged when image data recorded in areas with no watermarking information embedded has been tampered with, thus tampering being undetected.
Moreover, a uniform code information is used as electronic watermarking information and embedded into image data as it is or after encoded by a certain algorism. Such uniform code information is easily extracted once the embedding technique is detected. The embedded content is thus at a high risk of being detected even if it has been encoded.